Sulfolane-Based Electrolyte for High Voltage Li(Ni<sub>0.4</sub>Mn<sub>0.4</sub>Co<sub>0.2</sub>)O<sub>2</sub> (NMC442)/Graphite Pouch Cells
Notice bibliographique
Résumé
Introduction The development of high voltage Li-ion batteries is one of the best ways to increase their energy density. However, this simple approach has proven to be difficult since electrolyte solvents and additives are unstable at high potentials and the parasitic degradation of these components results in gas evolution, severe impedance growth, low coulombic efficiency (CE) and poor capacity retention [1-2]. Therefore, the development of high voltage electrolyte systems is one of the major bottlenecks in the path of lithium-ion cells with high energy density. In this presentation, the sulfolane (SL) – ethylmethyl carbonate (EMC) – vinylene carbonate (VC) system is shown to be viable in NMC442/graphite pouch cells that can be cycled at least to 4.5 V for several months. The introduction of electrolyte additives has been shown to improve battery performance indicators such as coulombic efficiency (CE), self discharge, etc. and while maintaining acceptable impedance when cells are cycled to high voltage. Long-term cycling results were also made to compare with 1 M LiPF6EC/EMC (3:7 wt.%) with and without additives. Experimental The pouch cells employed in this study were uncoated Li[Ni0.4 Mn0.4Co0.2]O2 (NMC442)/graphite cells with a capacity of 240 mAh and coated NMC442/graphite cells with a capacity of 180 mAh. The positive electrode material in the coated cells has been coated with 3 wt% of LaPO4 which appears as nanoparticles on the NMC particle surfaces. Both types of cells were balanced for 4.7 V operation. 1 M LiPF6EC/EMC (3:7 wt.% ratio, BASF, 99.99%) was used as the control electrolyte. The NMC442/graphite pouch cells were filled with 0.75 mL of electrolyte (0.90 g for EC:EMC electrolyte and 0.86 g for SL:EMC:2% VC electrolyte). The cells then underwent a formation protocol during which they were opened and re-vacuum sealed at 3.5 V and again at 4.5 V to remove any gas generated during the first charge. After formation, cells were moved to the Ultra High Precision Charger (UHPC). The cycling/storage procedure was as follows: cells were first charged to 4.400 V using currents corresponding to C/10, stored open circuit at 4.4 V for 20.00 h and then discharged to 2.800 V using currents corresponding to C/10. The cycling/storage procedure was designed so that the cells were exposed to higher potentials for significant fractions of their testing time. After these tests, cells were charged or discharged to 3.8 V where impedance spectra were measured. Results and discussion Figures 1 a-d compare the cycling/storage data collected on the UHPC for NMC442/graphite pouch cells containing 2% VC in SL:EMC:VC and “PES-211” in EC:EMC 3:7. Figures 1 a-d show the SL:EMC:VC system has similar delta V, discharge capacity, charge endpoint capacity slippage and CE to “PES-211” in EC:EMC 3:7. Figure 1e shows long-term cycling results for the unclamped NMC442/graphite pouch cells with control, “PES-211” in EC:EMC 3:7 and cells with 2% VC, 2% VC +1% MMDS, 2% VC + 2% PES and 2% VC +2% TAP in SL:EMC electrolyte. We can clearly see that cells containing 2% VC + 2% TAP in SL:EMC electrolyte show better cycling performance than cells with “PES-211” in EC:EMC 3:7. References L. Ma, J. Xia and J. R. Dahn, J. Electrochem. Soc., 161, A2250–A2254 (2014). L. Ma, J. Xia, and J. R. Dahn, Promising sulfur-containing electrolyte additives or ternary Electrolyte additive mixtures for Li-ion cells that promote long lifetime and better safety, 2015, submitted to J. Electrochem. Soc. Figure caption Figure 1. (a-d) The cycling data collected on the UHPC including DV, the charge endpoint capacity, the discharge capacity, and CE for NMC442/graphite pouch cells containing 2% VC in Sulfolane/EMC=3/7 system and PES-211 in EC/EMC=3/7 system. (e) Long-term cycling without clamps between 2.8 and 4.5 V at C/2.5 (100 mA) and 40 ± 0.1ºC with different additive sets in SL:EMC electrolyte. Figure 1
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».